In many catalytic hydrogenation processes applied to hydrocarbon oils, shale oil, tar sands, etc., of which hydrocracking and hydrotreating or hydrodesulfurization are typical examples, H.sub.2 S and NH.sub.3 are produced as a result of reaction of hydrogen with sulfur compounds and nitrogen compounds contained in the oil. Sometimes, this conversion of one or the other or both of the sulfur and nitrogen compounds is the desired reaction, while in other cases it is merely an incidental reaction. Normally, in a typical process, liquid hydrocarbon oil containing nitrogen compounds and sulfur compounds and recycle hydrogen-rich gas and makeup hydrogen are passed through a reaction zone, usually containing a catalyst, at elevated temperature and pressure at which at least a portion of the hydrocarbons are vaporized; and there is obtained as a reaction zone effluent a mixture of vaporized hydrocarbons, hydrogen, H.sub.2 S and NH.sub.3. The effluent may also contain heavier hydrocarbons which are liquid at the reaction conditions. The reaction effluent is cooled to condense vaporized hydrocarbons, whereby the liquid hydrocarbons can be separated from the hydrogen-rich recycled gas, which is then reused in the hydrogen process.
When the reaction effluent contains both H.sub.2 S and NH.sub.3, it has been found that on cooling to temperatures below about 300.degree.F, the H.sub.2 S and the NH.sub.3 may react to form salts which sometimes cause clogging problems in the heat exchangers and the lines. Injection of water into the reaction effluent upstream of the heat exchangers has been used to wash out such deposits and/or to prevent their formation. This water injection can provide a means of removing much of the ammonia formed if rather large amounts of water are injected sufficient to dissolve the ammonia.
While there are a number of known methods for separating mixtures of NH.sub.3 and H.sub.2 S from the aforesaid effluent, most of such methods involve scrubbing the gaseous phase produced in the hydrogenation step mentioned above with water. The resulting foul water stream contains primarily H.sub.2 S and NH.sub.3, both of which can be recovered from said foul water stream by subjecting the latter to steam stripping or the equivalent.
For conservation and ecological reasons, it is desirable to recover both H.sub.2 S and NH.sub.3 in useful form. Methods are known by which it is possible to separate the NH.sub.3 from H.sub.2 S; however, in many instances, operators do not find it economically justifiable to do so and dispose of such mixtures of H.sub.2 S and NH.sub.3 as a partial feed stream to a sulfur recovery unit. Uncontrolled operation using a stream of this kind of mixed feed has let to difficulties because the conditions used for combustion of H.sub.2 S to produce sulfur do not favor complete combustion of NH.sub.3. Even if only relatively small quantities, e.g., 200 ppm of NH.sub.3 remain in the combustion effluent gas which passes through the system, the presence of NH.sub.3 in such amounts constitutes a hazard because of its ability to react with SO.sub.3 to form ammonium sulfate at numerous locations in the plant and plug flow lines, seal pots, etc.